A cooling system for an internal combustion engine includes a thermostat which controls coolant flow from the engine proper to an air-cooled radiator. In addition, a vent hole is normally formed through an internal wall of the engine, mounting the thermostat thereon, to vent air to the radiator upon filling of the engine with coolant. In applications, such as school buses, wherein pick-up and delivery services require running of the bus at low idle approximately 60-70% of the time, the engine will tend to over-cool when ambient temperatures are in the range of 20.degree. F. and below. Such over-cooling of the engine will prevent the bus's heater from discharging sufficient heat to maintain the interior of the bus at an acceptably high temperature level, such as 65.degree. F.
One solution to this over-cooling problem is to substitute a vent valve in lieu of the continuously open vent hole which includes a movable valve element which will close an outlet from the vent valve after filling of the engine with coolant and venting of air therefrom. A vent valve of this type is disclosed in U.S. Pat. No. 4,052,965, issued on Oct. 11, 1977, to Charles S. Morris, and assigned to the assignee of this application. The vent valve is vertically disposed and the valve element thereof constitutes a spherical ball member which is adapted to move vertically upwardly to engage a valve set to close an outlet from the vent valve upon filling of the engine with coolant.
Any attempt to mount the vent valve horizontally in the engine could give rise to operational problems since inner surfaces of the housing of the vent valve, which intersect the frusto-conically shaped valve seat, would be disposed horizontally. Thus, premature closing of the vent valve could ensue. Furthermore, the abrupt angle change between such horizontally disposed inner surfaces and the valve seat could render it difficult for the ball member to expeditiously and efficiently close the outlet from the vent valve. In addition, the ball member may tend to remain in the area of the valve seat to thus prevent full opening thereof when the engine and the cooling system therefor are operational to purge the engine of air through the outlet from the vent valve.